Motor control circuit



July 25, 1950 Filed Aug. 3, 1945 MOTOR CONTROL CIRCUIT 3 Sheets-Sheet l CONTROLLED 5s OBJECT a T STATOR SYNCHRO CONTROL s4 ERRoR VOLTAGE FROM TRANSFORMER ROTOR 55 50 FROM 0.0. MOTOR STATOR 7 5 2 MASTER SYNCHRO T GENERATOR THYRATRON E D0 MOTOR CONTROL TO ROTOR APPARATUS MOTOR FIELD f M). POWER LINE 53 I 1 E; E

HHHHHIH 40 I A WW F B ER RoR E 3 VOLTAG E 2/ 5? E *souRcE l L. 11".": :L 3

AC PowER LINE MYRON G. PAWLEY y25, 1950 M. G. PAWLEY 2,516,144

MOTOR CONTROL CIRCUIT Filed Aug. 5, 1945 3 Sheets-Sheet 2 GRID BIAS VOLTAGEIEAB) 9 93 VOLTAGE FROMPOWER EAD LAG ANGLE(9|0) TRANSFORMER (EXY) EAD (EAB +Eco;E ac=OI VOLTAGES GOVERNING OPERATION OF TUBE IO (ERROR VOLTAGE ZERO) EFE (EFB+EcE-,Eac=OI EFE LAG ANGLE (an) GRID BIAS VOLTAGE (EFBI VOLTAGE FROM POWER TRANSFORMER (Em VOLTAG ES GOVERNING OPERATION OF TUBE II (ERROR VOLTAGE ZERO) MYRON G. PAWLEY u y 1950 M. G. PAWLEY 2,515,144

MOTOR CONTROL CIRCUIT Filed Aug. 5, 1945 5 Sheets-Sheet 5 TUBE /\GR|D BIAS voLTAGE FIREs AT (5A8) THIS TIME I TRYRAToN FIRING (SHADED AREA 0N POTENTIAL cURvE INDICATES TUBE Io Is VOLTAGES VS. TIME GRAPH SHOWING OPERATION -m 0F TUBE l0, ERRoR VOLTAGE PHASED TO FIRE TUBE l0 (REFER To FlG.6 FOR EQUIVALENT vEcToR DIAGRAM) Ill-EELS GRID BIAS Eco EXY VOLTAGE (EAB) ERROR VOLTAGE (E80) EAD WHEN ERRoR VOLTAGE IS ZERO (GIVE EAD LAG ANGLE IeIo) FoR REFERENCE) EAD (EAHEBHECD) VOLTAGES GovERNING OPERATIONS OF TUBE Io (ERROR voLTAGE PHASED To FIRE TUBE I0) I .T. E; 7

EFE

WHEN ERROR VOLTAGE EFE LAG ANGLHG") IS ZERO (FOR REFERENCE) EFE EcE (EFB+ EBG+ EcE) EYX GRID BIAs VOLTAGE 32! 324 32s ERRoR VOLTAGE (Esc) (EFB) voLTAGEs GovERNING OPERATION OF TUBE ll (ERROR VOLTAGE MYRON G. PAWLEY PHASED TO FIRE TUBE Io) Patented July 25, 1950 UNITED STATES PATENT OFFICE- MOTOR CONTROL CIRCUIT Myron G. Pawley, Alexandria, Va. lppllcation August 3, 1945, Serial No. 608,812

Claims. (01. 318-257) (Granted under the act of March 3, 1883, as amended April 30, 1928; 370 0. G. 757) This invention relates to rectifier systems; it is particularly directed to a system for controlling, by the use of grid-controlled, gas-filled rectifier tubes, the magnitude and direction of the current in a load circuit.

An object of the invention is to provide simple apparatus by which the magnitude and direction of the current flowing in a load circuit may be smoothly and continuously varied in response to a control voltage from a low power source.

Another object of the invention is to provide simple apparatus by which the speed and directlon of rotation of direct-current motors may be smoothly varied in response to control voltage from a low power source.

A further object of the invention is to provide apparatus possessing inherent anti-hunting and dynamic braking properties, for use in direct current motor control systems.

Still another object of the invention is to provide apparatus, simpler than heretofore practicablc, for remotely controlling the position of a motor-driven object.

Still a further object of the invention is to pro vide apparatus, simpler than heretofore practic able, by the use of which angular displacement introduced in control apparatus of small mass and inertia may be made to produce similar angular displacement to an object of great and inertia,

The invention comprises a novel rectifier sysusing grid-controlled rectifier tubes of the "type commonly called Thyratron. It is simpler and uses fewer components than previous systems directed to the some objects.

Further description oi the invention will be made with reference to the appended drawings, of which:

Figure l is a block diagram showing how the invention may be used, in conjunction with other apparatus, to achieve by electrical means remote control of the position of an object.

Figure 2 is a schematic diagram of an embodi ment of the invention, incorporating two thyra tron tubes, one therein denoted tube Hi; the other therein denoted tube l I. These tube designations are retained in the subsequent drawings.

Figure 3 is a vector diagram showing the relative magnitudes and phas relations of various voltages significant in analyzing the operation of tube l0.

Figure 4 is a vector diagram showing the relative magnitudes and phase relations of various voltages significant in analyzing the operation of tube H.

Figure 5 is a graph in Cartesian coordinates, with time as abscissa and voltage as ordinate, showing the variation as a function of time of various voltages significant in the operation of tube It under conditions difierent from those prevailing in Figure 3.

Figure 6 is a vector diagram showing vectorially most of the voltage data for tube l0 shown graphically in Figure 5.

Figure 7 is a vector diagram showing vectorially certain voltages pertinent to the operation of tube H under the conditions prevailing in Figures 5 and 6.

The block diagram in Figure 1 shows the invention as it might be incorporated in a system for electrical remote control of a rotating object. The invention to be described herein is shown in Figure l as blocl: 80, Thyratron Motor Gontrol Apparatus.

In the system of Figure 3 control of the rotation oi" controlled object 56 is achieved by rotation oi hand wheel 5i, which may be located at any dc sired distance from the controlled object. M chanically fixed to the shaft of hand wheel Si is the rotor of a synchro generator 50, the winding of which is supplied with alternating current from power line'iit. The stator windings of gen orator 50 are connected to the stator windings oi control transformer 5G. The rotor of control transformer 5 is mechanically fixed to the con trolled object 56 so that the rotor and controlled object rotate together. The rotor winding of control transformer 5*! is connected to the input of thyratroh motor control apparatus 80. D. 53., motor 55, mechanically coupled to controlled oh ject and control transformer 5 serves as the means by which they may be rotated. field winding oi motor 55 is supplied with constant excitation current by lit-C. source 52. The as mature winding of motor 55 is connected elec trically to the output of motor control apparatus 60. Motor control apparatus 68 derives its power from power line 53.

The mechanical coupling between the rotor oi control transformer 54 and controlled object it is so adjusted that when the controlled object is in the position desired relative to the position of handwheel 5!, no voltage is induced in the rotor winding of control transformer 5. If the controlled object be in any position other than the desired position, the rotor of control transformer 54 will not be in neutral position and a voltage will be induced in the rotor winding.

Hereinafter the angular deviation of the transformer rotor from its neutral or desired position 3 will be called "error angle"; the voltage appearing across the rotor winding of the control trans-. former will be called "error voltage."

The magnitude of the error voltage is proportional to the sine of the error angle; the errbr voltage will be in time phase with the power line voltage if the transformer rotor is on one side of "neutral" position and 180 out of phase with the power line voltage if it is on the other side of neutral.

The error voltage is applied to the thyratron motor control apparatus; and, responsively to the error voltage, the thyratron motor control apparatus supplies direct current to the armature of motor it. The direction of rotation of motor 55 depends upon the direction of current flow through its armature; the current supplied will be of that direction, as required by the phase of the error voltage, which will cause the motor's rotation to reduce the error angle. When the motor has moved the controlled object and the control transformer rotor sufllciently to reduce the error angle to zero, the error voltage drops to zero; direct-current output of the control apparatus becomes zero;v and the motor stops. The control apparatus, which constitutes the invention herein, possesses inherent dynamic braking and anti-hunting characteristics which tend to prevent the controlled object from overshoot- .ing" the position of zero error voltage.

The foregoing description of the D.-C. follower type of motor control system is included herein to show clearly how the apparatus constituting this invention may be used in conjunction with other apparatus in a frequently-em-- ployed control application. It is of course exemplary only and does not purport to define the range of the possible applications of this invention. In other applications the error voltage" which governs the action of the invention might come from any source.

Figure 2 shows in schematic form an exemplary embodiment of the invention. In this embodiment the load fed by the jjcontrol apparatus is a D.-C. motor i. The field winding 3 of motor iis supplied with constant excitation current from D.-C. source 6. One terminal of armature 2 of motor i is connected to terminal Y of secondary winding 24 of transformer l. The other terminal of armature 2 is connected through choke coil 5 to the plate of thyratron tube ll. 'l'he'oth'er terminal of secondary winding 24 of transformer 4, marked X on Figure 2, is connected to the plate of thyratron tube ill. Primary winding ll of transformer l is connected to A.-C. power line I. The plate of tube It is connected to the cathode of tube l l, and the plate of tube ii is connected to the cathode of tube It. The cathode of tube III is marked D; the cathode of tube ii is marked E. The cathodes of tubes III and II are connected together through high resistances l and 9, which are of equal size, so that point C, at the junction of resistors 8 and 0, is the electrical midpoint between the two cathodes. Tubes I. and II are identical thyratron rectifier tubes.

The primary winding of grid bias transformer lll is connected in series with variable resistor it across power line 1. Secondary winding 3| of transformer II is center tapped at point B; one terminal of secondary winding 30, marked 4, is connected through resistor I: to the grid of It; the. other terminal of secondary wind- I it, marked F, is connected through resistor if to the grid'of tube ll. Resistors i2 and I;

. 4' are grid-current limiting resistors; there is no voltage drop across resistor it when the grid of tube It is negative relative to its cathode; likewise there is no voltage drop across resistor [2 when the grid of tube II is negative relative to its cathode.

Point 3, the center tap of secondary winding 30, is connected to point C, the junction of resistors 8 and 8, through secondary winding 35 of error voltage transformer ii. The primary winding 25 of transformer i5 is connected to errorvoltage source l9. Error-voltage source i9 is shown as a block connected to A-C. line '5, since its form will vary according to the character of the application. For purposes of this specification, it may be considered to be any source of alternating voltage of variable amplitude, of the same frequency as that of power line i and either identical in phase to the voltage of the power line or 180 out of phase with the power line voltage, depending on the direction of load current flow desired.

Referring toFigures 3 and 4, the operation of the invention will first be described for the case where voltage from the error voltage source is zero. When the tubes to and ii are non-conducting, the current fiow through motor armature 2 and smoothing choke 5 is so small as to be negligible, since resistors 8 and 9 have very high resistance. When both tubes are non-conducting, therefore, the voltage of secondary winding 24 of transformer 4 is applied from plate to cathode of tube ill. Likewise the same voltage appears in opposite phase between plate and cathode of tube i I. The voltage across the winding 24 is called ExY or EYx, depending on whether it is being considered as the voltage of point X with respect to point Y or the voltage Y with respect to X. Exr is represented in Figure 3 as vector 9 1; Ex is represented in Figure 4 as vector illl.

. Since resistors 8 and 9 are equal, the voltage from point C to point D across resistor 8, hereinafter called Eon, is in phase with Em? and half as great in magnitude. Likewise the voltage from point C to point E across resistor 9, hereinafter calledEcn, is in phase with Evx and half as great in magnitude. Eon is shown on Figure 3 as vector i 92; E05: is shown on Figure 4 as vector I 02.

' with respect to its center tap B, are hereinafter called EAB and Ere respectively. Resistor IS in the primary circuit of transformer 40, acting in coniunction with the leakage inductance of primary winding 20, causes the voltage across primary winding 20 to lead the power line voltage in phase by about 15. The connections to secondary winding 30 are so chosen that Eng lags .ExY by about and voltage Ere lags Erx by a like amount. The exact phase shift introduced by resistor I6 is not critical; the value of 15 gave excellent results in a practical construction of the invention. The amplitudes of Ean and En; are likewise not critical, although they should be of the same order of magnitude as ExY. In this embodiment the magnitudes. of EAB and En; are each equal to that of Exit. vElna is represented on Figure 3 as vector 93; En is shown on Figure 4 as vector I03.

The voltage between point B, the center tap of In the present discussion, the error voltage is assumed to be zero, hence Enc is zero.

The alternating voltages contributing to the grid-cathode voltage of tube II are EAB, E30, and Eon. The voltage EA!) is the vector sum of the three last named voltages and is the grid-cathode voltage of tube In except insofar as the flow of grid current through resistor II causes grid-limiting to occur. That is, the grid-cathode voltage of tube In is identical to Em during its negative hall-cycles, but the grid does not follow Em during its positive half-cycles, remaining limited at a voltage slightly above zero. Es for the present discussion is the vector sum of EA}; and Ecp, since Ego is zero, and is represented on Figure 3 as vector 94. l

The alternating voltages making up the gridcathode voltage of tube II are Ens, Em, and Eon. The voltage Em is the vector sum of these voltages, and but for the limiting eflect caused by grid current flow through resistor li when Em is positive, Em is the grid-cathode voltage of tube I I. Era is the vector sum of Era and Ear: when Eco equals zero, and is represented on Figure 4 as vector let. I

as can be seen by reference to Figure 3, the voltage EAD, impressed on the grid circuit of tube ill, lags Exv, applied in the plate circuit-oi tube it, by an angle die, which is about 150. Likewise, as shown in Figure 4, voltage Ere, impressed on the grid circuit of tube ii, lags Eyx', applied in the plate circuit of tube H, by an angle 61;, also about 01c and on are equal when the error voltage is zero.

These phase angles sis-and 011 are such, when the error voltage is zero, that the grid ofeach tube rises above the critical ionization or firing potential just before the end of the positive hall cycle of plate circuit voltageExv for tube 118, Em for tube il. in consequence each tube conducts for small part of each cycle; Em and Eva: are opposite in phase; accordingly, tube it conducts for a brief period at the end of one halibcycle, and tube ll conducts for a similar period at the end of the next half cyclc, and-so on. The re suit is a small alteruatlng current flowing in the load circuit. Since the average value oi thiscur re t zero, it does not cause; armature 2 to ro- So long the error voltage equals zero, the motor is motionless.

Nov; assume the external conditions are so al tcreol to produce an error voltage the pri mary W cling of transformer l5. E80, the voltage across the secondary winding of transformer it, costumes 2. value other than zero and is added vcc t-oriall to both and As a result the ol temutiue voltage in the grid circuit of one of the tubes will advance in phase and shrink in ampli tude, thus causing that tube to conduct earlier in the cycle than beiorc. The alternating voltage in. thegrid circuit of the-other tube will be retarded in phase and increased in amplitude; so the other tube will lire later in the cycle, or not at all if the error voltage be large. In consequence a not direct current flow through the motor armature; and the motor will rotate in one direction or the other depending on which tube is firing first. Reversal of the phase of the error voltage will interchange the roles of the two tubes, cause the armature current to reverse, and thus reverse the motors direction of, rotation.

Figure 5 is a voltage vs. time graph which shows the operation of tube It for a case wherein the error voltage is phased to advance the firing time tion with Figure 6, which is an equivalent vector diagram. Each vector on Figure 6 bears an identitlcation number 100 units larger than the identification number of the corresponding curve on Figure 5; that is, vector I on Figure 6 corresponds to curve I2I on Figure 5, etc.

On Figure 5, curve III shows the variations with time of En, applied in the plate circuit of tube Ill. Curve I24 is Eco, half as great in amplitude as Exy and in phase with it. Curve I23 is Eac, the error voltage; it is in phase with Eon. The voltage E a, from the grid bias transformer, is shown as curve I22, equal in amplitude to En and almost 180 out or phase with it. The voltage EAD, which is the vector sum of the three voltages Ears, E80, and Eon, is the net voltage impressed till '- effects tends to retard the on the grid circuit or tube It and is shown as curve I21. Curve I26 is the instantaneous value of the thyratron firing voltage, plotted as a function of time. When the grid-cathode voltage becomes more positive than the firing voltage, that is, at intersection of curves I21 and I28, the gas in the tube ionizes and for the remainder of the half cycle of Exv the tube conducts. These conducting periods are indicated by the shaded areas I28. During these conducting periods the platecathode potential oi tube I0 drops to a very low value and the voltage Exr appears across armature 2 and smoothing inductance E.

Figure 6 and Figure 'I, considered together, con trast the operation of the two tubes when an error voltage is present. Vector t l from Figure 3, which represents Em, the grid circuit voltage of tube III for zero error voltage, has been incorpo rated in Figure 6 for reference. Note from Fig ure 8 that the addition of Eec to the grid circuit voltage of tube it results in a new E's]: vector 22l which is reduced in amplitude compared to vee tor 84. Also note that the lag angle 6'10 between. the grid circuit voltage and the circuit volt= ages is smaller than before. Each of these efiects tends to advance the firing time or tube i0.

Vector Hit, representing the grid circuit voltage of tube H for zero error voltage, has been incorporated in Figure 'l for reference. Note from Figure E that voltage EEC is bucking result-- ingin a new vector 321i, which larger in amplitude than vector ltd. Also note that the lag angle 011 is larger than before Each oi these oitube ll.

Ii the error voltage applied s ausloruier ill were reversed in phase, tulle ll would conduct earlier in each cycle than with no error voltage and tube it would conduct later, with the result that the direction of the c current would reverse. The magnitude or the .verage current through the armature is appro oatelv propos tional to the magnitude of the en 91. voltage. Cori-- sequentlv', by use of this invention, the motor may be reversed or smoothly varied in: speed by con trol of the magnitude and phase of the error voltage. The error voltage source not require-o2 to supply any appreciable amount of power, and the total error voltage required is small.

This invention possesses inherent anti-hunting and dynamic braking characteristics which make it well suited for use in a system such as that shown in block iorm in Figure 1. When the motor is rotating, its 11-0. back. electromotive force is impressed across resistors 8 and 9, thus intro ducing into the grid circuits oi the thyratrons a D.-C. voltage of such polarity as to oppose the firing of the tube which is passing the armature current. In consequence, it the error voltage oi tube it. Figure 5 may be examinedinconnecdrops, the 11-0. voltage from the motors back EMF. takes control, prevents the previously conducting tube from passing any more current and accelerates the firing of the other tube, thus passing current through the armature in the opposite direction and quickly braking the motor. The overall result is a heavily damped system which starts and stops smoothly and has no tendency to oscillate around a rest position.

It will be understood that the embodiment of the invention described herein is exemplary only, and that the scope of the invention is to be determined from the appended claims.

The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

What is claimed is:

1. In combination, a pair of grid-controlled, gas-filled rectifier tubes, each having a cathode, an anode, and a grid; means connecting the anode of each tube to the cathode of the other; an alternating power supply connected across the tubes to form a controlled power circuit; load means connected in series in said controlled power circuit; means including a phase shift circuit coupling an alternating voltage to the grid of each tube lagging the anode voltage applied thereto by more than-90 and less than 180; and means for introducing a voltage in like phase to both grids to vary the relative conduction of the tubes.

.2. In combination, a pair of grid-controlled,

gas-filled rectifier tubes, each having a cathode, an anode, and a grid; means connecting the anode of each tube to the cathode of the other; an alternating power supply connected across the tubes to form a controlled power circuit; load means connected in series in said controlled power circuit; means in said controlled power circuit operative to supply a grid bias voltage to the grid of each tube in phase with its anode voltage; means including a phase shift circuit for supplying to the grid of each tube an additional voltage lagging its anode voltage by more than 90 and less than 180; and means for introducing a voltage in like phase to both grids to vary the relative conduction of the tubes.

3. In combination, a pair of grid-controlled, gas-filled rectifier tubes, each having a cathode, an anode, and a grid; means connecting the anode of each tube to the cathode of the other; an alternating power supply; a load element connected in series with the tubes across the power supply; impedance means connected between the cathodes; first alternating bias voltage supply means connected between the mid-point of said impedances means and the. grid of one of the tubes;

second alternating bias voltage supply means connected between said mid-point and the grid of the other tube each alternating voltage bias supply means providing a biasing voltage lagging to respective anode voltage by more than 90 and less rect-current motor; means supplying the motor with constant field excitation; means connecting the motor armature in series with the tubes across the power supply; impedance means connected between the cathodes; means including a phase shift circuit supplying an alternating bias voltage to the grid of each tube lagging the respective anode voltage by more than and less than a source'of alternating control voltage coupled in like phase to both grids; and means operable to vary the amplitude and phase of the control voltage to vary the relative conduction of the tubes, and thereby to vary the magnitude and direction of the current fed to the motor armature.

5. A motor control system comprising a pair of grid-controlled, gas-filled rectifier tubes, each having a cathode, an anode, and a grid; means connecting the anode of each tube to the cathode of the other; an alternating power supply; a direct-current motor; means supplying the motor with constant field excitation; means connecting the motor armature in series with the tubes across the power supply; impedance means connected between the cathodes; phase-shifting means; a bias transformer having a primary winding and a center-tapped secondary winding, the primary winding being connected to the power supply through the phase shifting means and the terminals of the secondary winding being connected to the respective grids of the tubes; a source of alternating control signal connected between the center-tap of the bias transformer secondary winding and the midpoint of said impedance means; and means for varying the control signal to? control the speed of the motors rotation and the direction of its rotation.

- MYRON G. PAWLEY.

REFERENCES CITED 'I 'he following references are of record in th file of this patent:

UNITED STATES PATENTS Number Name Date 1,924,459 Ryder Aug. 29, 1933 1,977,624 Davis Oct. 23, 1934 2,293,502 Herrmann Aug. 18, 1942 2,399,695 Satterlee May 7, 1946 

